Method of enhancing hardness of sputter deposited copper films

ABSTRACT

The present invention provides a method and apparatus for forming a copper layer on a substrate, preferably using a sputtering process. The sputtering process involves bombarding a conductive member of enhanced hardness with ions to dislodge the copper from the conductive member. The hardness of the target may be enhanced by alloying the copper conductive member with another material and/or mechanically working the material of the conductive member during its manufacturing process in order to improve conductive member and film qualities. The copper may be alloyed with magnesium, zinc, aluminum, iron, nickel, silicon and any combination thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of co-pending U.S. patentapplication Ser. No. 09/518,004, filed Mar. 2, 2000 which is acontinuation-in-part of U.S. patent application Ser. No. 09/406,325,filed on Sep. 27, 1999. Each of the aforementioned related patentapplications is herein incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to the deposition of a layer on asubstrate. More specifically, the invention relates to deposition of adoped layer on a substrate.

[0004] 2. Description of the Related Art

[0005] Consistent and fairly predictable improvement in integratedcircuit design and fabrication has been observed in the last decade. Onekey to successful improvements is multilevel interconnect technology,which provides the conductive paths between the devices of an integratedcircuit (IC) and other electronic devices. The conductive paths, orfeatures, of an IC typically comprise horizontal interconnects (alsoreferred to as lines) and vertical interconnects (also referred to ascontacts or vias). The shrinking dimensions of features, presently inthe sub-quarter micron range, has increased the importance of reducingcapacitive coupling between interconnect lines and reducing resistancein the conductive features.

[0006] Aluminum has traditionally been the choice of conductivematerials used in metallization. However, smaller feature sizes havecreated a need for a conductive material with lower resistivity thanaluminum. Copper is now being considered as an interconnect material toreplace or complement aluminum because copper has a lower resistivity(1.7 μΩ-cm compared to 3.1 μΩ-cm for aluminum) and higher currentcarrying capacity.

[0007] As a result of the desirability of using copper for semiconductordevice fabrication, current practice provides for sputtering high puritycopper targets. High purity is considered desirable in order to ensurethat the low resistivity of copper is not affected by contaminants.However, the inventors have discovered that high purity copper filmssuffer from electromigration. Electromigration refers to the soliddiffusion of ions in the presence of electric fields. Atoms in aconductive material are displaced as a consequence of a direct momentumtransfer from the conduction electrons in the direction of their motion.The large flux of electrons interacts with the diffusing atoms in themetal lattice and sweeps these atoms in the direction of electron flow.The transport of mass causes removal of material in some locations,which generates voids and the accumulation of material in otherlocations. As a result, electromigration causes failures by openinginterconnect lines.

[0008] Therefore, there is a need for an improved copper based targetmaterial which mitigates the problems of electromigration.

SUMMARY OF THE INVENTION

[0009] The present invention generally provides a method and apparatusfor forming a target material having enhanced hardness. The targetmaterial is well suited for sputtering processes wherein a portion ofthe material is deposited on a substrate such as by physical vapordeposition (PVD) or Ionized Metal Plasma (IMP) PVD.

[0010] In one aspect, the invention provides a method of sputtering alayer on a substrate, comprising generating a plasma in a substrateprocessing chamber, sputtering material from a conductive target, thetarget comprising a material having a vickers hardness between about 100and about 250, and depositing the sputtered material on the substrate.In one embodiment, the target includes copper and another materialselected from the group of magnesium, zinc, aluminum, iron, nickel,silicon and combinations thereof.

[0011] In yet another aspect, a conductive material having enhancedhardness is deposited on a substrate. The material comprises at leastcopper and has a vickers hardness of between about 100 and about 250. Inone embodiment, the material comprises primarily copper combined withanother material selected from the group of magnesium, zinc, aluminum,iron, nickel, silicon and combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] So that the manner in which the above recited features,advantages and objects of the present invention are attained and can beunderstood in detail, a more particular description of the invention,briefly summarized above, may be had by reference to the embodimentsthereof which are illustrated in the appended drawings.

[0013] It is to be noted, however, that the appended drawings illustrateonly typical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

[0014]FIG. 1 is a schematic cross-sectional view of an IMP chamber.

[0015]FIG. 2 is a schematic cross-sectional view of a substrate with aseed layer formed on the substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] The present invention provides a method and apparatus for forminga copper layer on a substrate, preferably using a sputtering process.The sputtering process involves bombarding a conductive member ofenhanced hardness with ions to dislodge the copper from the conductivemember. The hardness of the target may be enhanced by alloying thecopper conductive member with another material and/or mechanicallyworking the material of the conductive member during its manufacturingin order to improve conductive member and film qualities. As referred toherein “working” refers to any process by which a material is treated,conditioned or otherwise processed to affect the qualities, e.g.hardness, of the material. Illustratively, the following descriptionrefers to the conductive member as a target, which typically providesthe bulk of the material to be deposited on a substrate. However, theconductive member may be any component which is sputtered andcontributes to the deposition of material on the substrate.

[0017] The inventors have discovered that qualities such as thehardness, grain size, crystallographic orientation, etc. of targetmaterials affect the quality of the resulting film produced bysputtering the target as well as the sputtering characteristics of thetarget. According to the invention, such qualities and characteristicscan be affected by the methods and materials used to manufacture thetarget. As an example, the susceptibility of the deposited film toelectromigration can be reduced. Additionally, microarcing on thesurface of the target during sputtering can be mitigated.

[0018] Solid metals are typically composed of separate and discreetgrains of continuous crystal lattice rather than one continuous crystalstructure. Depending on the composition and forming method of the metal,these grains can vary in size from the millimeter range to the micronrange. By providing targets having smaller grain size the inventionmitigates the problems of electromigration and microarcing.

[0019] Another factor which affects microarcing on the target surfaceand the electromigration characteristics of the deposited material, isthe crystallographic orientation of the grains. Each grain is acontinuous crystal, with its crystal lattice oriented in some particularway relative to a reference plane such as the sputtering surface of thetarget. Since each grain is independent of others, each grain latticehas its own orientation relative to this plane. When grain orientationis not random and crystal planes tend to be aligned in some way relativeto a reference plane, the material is said to have “texture”. Thesetextures are noted using standard indices which define directionsrelative to crystallographic planes. For instance, a target made from ametal with cubic crystal structure, such as copper, may have a <100>, a<110> or other textures. The exact texture developed will depend on themetal type and the work and heat treatment history of the target.

[0020] In one embodiment, a copper target is alloyed with anothermaterial (herein referred to as the alloy) to increase the hardness ofthe target. The target is preferably made of copper and an alloyselected from the group of magnesium, zinc, aluminum, iron, nickel,silicon and any combination thereof. The percentage by weight of thealloy is from about 0.01% to about 10%, and most preferably from about0.01% to about 5%. In one embodiment, the vickers hardness of the targetis between about 100 and about 250.

[0021] A number of processes known to metallurgists can be adapted toproduce a copper-alloy target. The target can be prepared, for example,by uniformly mixing the alloy into a molten copper material which isthen cast and cooled to form the target. The alloy material may beprovided in the form of a pellet which is then added to the moltencopper. By alloying the copper target in such a manner, it is believedthe hardness of the target can be enhanced. The inventors havediscovered that a target of enhanced hardness mitigates the problems ofelectromigration associated with the prior art high purity coppertargets. Further, even where the alloy material has a higher resistivitythan copper, such as where aluminum is used to alloy the copper target,the effect on the resistivity of the resulting film formed on thesubstrate is minimal because of the relative proportions of the alloy tothe copper.

[0022] The copper-alloy target of the invention can then be sputtered toform a copper alloy film on a substrate. The resulting alloyed filmexhibits superior resistance to electromigration. In one application,the target can be sputtered to produce a seed layer on features formedon a substrate. The substrate may then undergo various additionalprocesses including an electroplating process wherein the features arefilled with a material, such as copper. It is believed that a portion ofthe alloy material diffuses into the fill material. As a result, thefill material is made more resistant to electromigration. Even thoughthe alloy material will typically have a higher resistivity than copper,the amount of alloy used, by weight percentage of the target, is minimalcompared to the weight percentage of copper in the target. Thus, theeffect on the overall resistivity is negligible. The proper proportionsof alloy to be combined with the copper during the manufacturing of thetarget can be determined by the volume of the features to be filled,thereby ensuring that sufficient alloy is diffused into the fillmaterial without compromising the resistivity of the deposited material.

[0023] In another embodiment, the hardness of a copper target isincreased by mechanically working the target material(s) bymetallurgical methods. Work hardening the target allows the grain sizeof the target material to be changed to produce a relatively hardertarget. In a preferred embodiment, a copper-alloy target has a vickershardness between about 100 and about 250. Illustratively, methods ofmanufacturing a copper-alloy target include casting, forming, annealing,rolling, forging, liquid dynamic compaction (LDC), equal channel angularextrusion (ECA) and other methods known and unknown in metallurgy.Although one embodiment of the invention contemplates using knownmetallurgical methods, such methods have heretofore not been used in theproduction of copper-alloy targets for the purpose of enhancing theirhardness.

[0024] The copper-alloy target of the invention can be utilized in anysputtering chamber. One such sputtering chamber is the Ionized MetalPlasma (IMP) Vectra™ chamber, available from Applied Materials, Inc. ofSanta Clara, Calif. An IMP process provides a higher density plasma thanstandard PVD that causes the sputtered target material to becomeionized. The ionization enables the sputtered material to be attractedin a substantially perpendicular direction to a biased substrate surfaceand to deposit a layer within high aspect ratio features.

[0025]FIG. 1 is a schematic cross-sectional view of an IMP chamber 100,capable of generating a relatively high density plasma, i.e., one with acapability to ionize a significant fraction of both the process gas(typically argon) and the sputtered target material. The chamber 100includes sidewalls 101, lid 102, and bottom 103. The lid 102 includes atarget backing plate 104 which supports a target 105 of the material tobe deposited.

[0026] An opening 108 in the chamber 100 provides access for a robot(not shown) to deliver and retrieve substrates 110 to and from thechamber 100. A substrate support 112 supports the substrate 110 in thechamber and is typically grounded. The substrate support 112 is mountedon a lift motor 114 that raises and lowers the substrate support 112 anda substrate 110 disposed thereon. A lift plate 116 connected to a liftmotor 118 is mounted in the chamber 100 and raises and lowers pins 120a, 120 b mounted in the substrate support 112. The pins 120 a, 120 braise and lower the substrate 110 from and to the surface of thesubstrate support 112.

[0027] A coil 122 is mounted between the substrate support 112 and thetarget 105 and provides inductively-coupled magnetic fields in thechamber 100 to assist in generating and maintaining a plasma between thetarget 105 and substrate 110. The coil 122 is also sputtered due to itslocation between the target and the substrate 110 and preferably is madeof similar constituents as the target 105. Thus, the coil comprisescopper and an alloy selected from the group of magnesium, zinc,aluminum, iron, nickel, silicon and any combination thereof. The alloypercentage of the coil 122 could vary compared to the target alloypercentage depending on the desired layer composition and is empiricallydetermined by varying the relative weight percentages. Power supplied tothe coil 122 provides an electromagnetic field in the chamber 100 thatinduces currents in the plasma to increase the density of the plasma,thereby enhancing the ionization of the sputtered material. The ionizedmaterial is then directed toward the substrate 110 and depositedthereon.

[0028] A shield 124 is disposed in the chamber 100 to shield the chambersidewalls 101 from the sputtered material. The shield 124 also supportsthe coil 122 by coil supports 126. The coil supports 126 electricallyinsulate the coil 122 from the shield 124 and the chamber 100 and can bemade of similar material as the coil. The clamp ring 128 is mountedbetween the coil 122 and the substrate support 112 and shields an outeredge and backside of the substrate from sputtered materials when thesubstrate 110 is raised into a processing position to engage the lowerportion of the clamp ring 128. In some chamber configurations, theshield 124 supports the clamp ring 128 when the substrate 110 is loweredbelow the shield 124 to enable substrate transfer.

[0029] Three power supplies are used in this type of sputtering chamber.A power supply 130 delivers preferably DC power to the target 105 tocause the processing gas to form a plasma, although RF power can beused. Magnets 106 a, 106 b disposed behind the target backing plate 104increase the density of electrons adjacent to the target 105, thusincreasing ionization at the target to increase the sputteringefficiency. The magnets 106 a, 106 b generate magnetic field linesgenerally parallel to the face of the target, around which electrons aretrapped in spinning orbits to increase the likelihood of a collisionwith, and ionization of, a gas atom for sputtering. A power supply 132,preferably a RF power supply, supplies electrical power to the coil 122to couple with and increase the density of the plasma. Another powersupply 134, typically a DC power supply, biases the substrate support112 with respect to the plasma and provides directional attraction (orrepulsion) of the ionized sputtered material toward the substrate 110.

[0030] Processing gas, such as an inert gas of argon or helium or areactive gas such as nitrogen, is supplied to the chamber 100 through agas inlet 136 from gas sources 138, 140 as metered by respective massflow controllers 142, 144. A vacuum pump 146 is connected to the chamber100 at an exhaust port 148 to exhaust the chamber 100 and maintain thedesired pressure in the chamber 100.

[0031] A controller 149 generally controls the functions of the powersupplies, lift motors, mass flow controllers for gas injection, vacuumpump, and other associated chamber components and functions. Thecontroller 149 controls the power supply 130 coupled to the target 105to cause the processing gas to form a plasma and sputter the targetmaterial. The controller 149 also controls the power supply 132 coupledto the coil 122 to increase the density of the plasma and ionize thesputtered material. The controller 149 also controls the power supply134 to provide directional attraction of the ionized sputtered materialto the substrate surface.

[0032] The controller 149 preferably comprises a central processing unit(CPU), a memory, and support circuits for the CPU. To facilitate controlof the chamber, the CPU may be one of any form of general purposecomputer processor that can be used in an industrial setting forcontrolling various chambers and subprocessors. The memory is coupled tothe CPU. The memory, or computer-readable medium, may be one or more ofreadily available memory such as random access memory (RAM), read onlymemory (ROM), floppy disk drive, hard disk, or any other form of digitalstorage, local or remote. The support circuits are coupled to the CPUfor supporting the processor in a conventional manner. These circuitsinclude cache, power supplies, clock circuits, input/output circuitryand subsystems, and the like. A deposition process is generally storedin the memory, typically as a software routine. The software routine mayalso be stored and/or executed by a second CPU that is remotely locatedfrom the hardware being controlled by the CPU of the controller 149.

[0033] In one embodiment, a seed layer is deposited on a substrate bysputtering the target 105. A noble gas, such as helium or argon, isflown into the chamber at a rate sufficient to produce a chamberpressure of about 5 to about 100 mTorr, preferably about 20 mTorr toabout 50 mTorr. The power supply 130 delivers about 200 Watts (W) toabout 12 kW, preferably about 750 W to about 3 kW to the target 105. Thepower supply 132 delivers an AC signal to the coil 122 between about 500W and about 5 kW, and preferably about 1.5 kW to about 2.5 kW. The powersupply 134 delivers about 0 W to about 600 W, preferably about 350 W toabout 500 W to the substrate support 112 with a duty cycle between 0% to100% and preferably about 50% to about 75%. When the substratetemperature is controlled, a surface temperature between about −50° C.to about 150° C., preferably below 50° C. is useful for processingduring the seed layer deposition. The sputtered target material isdeposited on the substrate to a thickness of about 500 Å to about 4000Å, preferably about 2000 Å.

[0034] The above parameters are preferably used to deposit a layer on a200 mm substrate and are not intended to be limiting. For example, powerdensities may be determined from the given power ranges and scaled up tolarger substrates, such as 300 mm substrates, or down to smallersubstrates, such as 100 mm substrates.

[0035] Further, although the chamber described above is an IMP chamberother chambers may be used. Thus, in one embodiment, the target 105 isdisposed in a PVD chamber. In some cases, the above described parametersare dependent on the particular chamber type. For example, in oneembodiment utilizing a PVD chamber, the power level delivered to thetarget 105 by the power supply 130 is between about 200 W to about 12kW. In an embodiment utilizing an IMP chamber, the power level deliveredto the target 105 by the power supply 130 is between about preferablyabout 750 W to about 3 kW.

[0036]FIG. 2 is a schematic cross-sectional view of an exemplarysubstrate 110 formed according to a process of the invention. Adielectric layer 204 is deposited on the substrate 110 and etched toform the feature 200, such as a via, contact, trench or line. The term“substrate” is broadly defined as the underlying material and caninclude a series of underlying layers. The dielectric layer 204 can be apre-metal dielectric layer deposited over a silicon wafer or aninterlevel dielectric layer.

[0037] A liner layer 206, such as a Ta layer, is deposited on thedielectric layer 204 as a transition layer to promote adhesion to theunderlying material and reduce contact/via resistance. The liner layer206 is preferably deposited using an IMP PVD process and can bedeposited by other PVD processes, such as collimated or long throwsputtering or other methods such as CVD. Collimated sputtering isgenerally performed by placing a collimator (not shown) between thetarget and the substrate to filter sputtered material travelingobliquely through the collimator. Long throw sputtering is generallyperformed by increasing the spacing between the target and thesubstrate. The increased distance increases the probability that thesputtered material reaching the substrate is directed normal to thesubstrate surface. A barrier layer 208 of tantalum nitride (TaN) isdeposited on the liner layer 206 using PVD, and preferably an IMP PVDprocess, especially for high aspect ratio features. The barrier layerprevents diffusion of copper into adjacent layers. While Ta/TaN arepreferred, other liner and/or barrier layers that can be used aretitanium (Ti), titanium nitride (TiN), tungsten (W), tungsten nitride(WN) and other refractory metals and their nitrided counterparts.

[0038] A seed layer 210 is deposited over the TaN barrier layer 208,using PVD and preferably IMP PVD. The seed layer 210 is deposited bysputtering a copper/copper-alloy target of the invention. The seed layer210 is deposited over the barrier layer 208 as a seed layer for asubsequent copper fill 212.

[0039] The copper fill 212 can be deposited by PVD, IMP, CVD,electroplating, electroless deposition, evaporation, or other knownmethods. Preferably, copper fill 212 is deposited using electroplatingtechniques. Subsequent processing can include planarization by chemicalmechanical polishing (CMP), additional deposition of layers, etching,and other processes known to substrate manufacturing.

[0040] The hardened target material of the invention is believed toreduce the potential for electromigration during operation of thedevices formed on the substrate 110 surface. Additionally, empiricalevidence suggests that harder targets result in reduced arcing betweenthe target and an adjacent structure, where the arcing dislodgesunwanted pieces of the target (splats) that are deposited on thesubstrate and contaminates the deposition.

[0041] Variations in the orientation of the chambers and other systemcomponents are possible. Additionally, all movements and positions, suchas “above,” “top,” “below,” “under,” “bottom,” “side,” described hereinare relative to positions of objects such as the target, substrate, andcoil. Accordingly, it is contemplated by the present invention to orientany or all of the components to achieve the desired support ofsubstrates in a processing system.

[0042] While the foregoing is directed to the preferred embodiment ofthe present invention, other and further embodiments of the inventionmay be devised without departing from the basic scope thereof and thescope thereof is determined by the claims that follow.

1. A method of depositing a seed layer over a surface of a substrate,comprising: depositing a copper alloy seed layer over a surface of asubstrate at a substrate temperature between about −50° C. and about150° C., the copper alloy seed layer comprising an alloying materialselected from the group of aluminum, magnesium, and combinationsthereof, the alloying material being present in the copper alloy seedlayer in a concentration between about 0.01 weight percent and about 10weight percent.
 2. The method of claim 1, wherein the copper alloy seedlayer is deposited at a substrate temperature less than about 50° C. 3.The method of claim 1, wherein the copper alloy seed layer is depositedby physical vapor deposition.
 4. The method of claim 3, wherein thecopper alloy seed layer is deposited by utilizing a high density plasma.5. The method of claim 1, wherein the alloying material is present inthe copper alloy seed layer in a concentration between about 0.01 weightpercent and about 5 weight percent.
 6. A method of forming a feature,comprising: depositing a barrier layer over a surface of a substrate;and depositing a copper alloy seed layer over the barrier layer, thecopper alloy seed layer comprising an alloying material selected fromthe group of aluminum, magnesium, and combinations thereof, the alloyingmaterial being present in the copper alloy seed layer in a concentrationbetween about 0.01 weight percent and about 10 weight percent.
 7. Themethod of claim 6, wherein the barrier layer comprises a materialselected from the group consisting of tantalum nitride, tantalum,titanium, titanium nitride, tungsten, tungsten nitride, other refractorymetals, other refractory metal nitrides, and combinations thereof. 8.The method of claim 6, further comprising depositing a bulk copper layerover the copper alloy seed layer.
 9. The method of claim 8, wherein thebulk copper layer is deposited by electroplating.
 10. The method ofclaim 6, wherein the copper alloy seed layer is deposited at a substratetemperature between about −50° C. and about 150° C.
 11. The method ofclaim 10, wherein the copper alloy seed layer is deposited at asubstrate temperature less than about 50° C.
 12. The method of claim 6,wherein the alloying material is present in the copper alloy seed layerin a concentration between about 0.01 weight percent and about 5 weightpercent.
 13. A method of forming a feature, comprising: depositing abarrier layer comprising tantalum nitride; depositing a copper alloyseed layer over the barrier layer, the copper alloy seed layercomprising aluminum present in the copper alloy seed layer in aconcentration between about 0.01 weight percent and about 10 weightpercent; and depositing a bulk copper layer over the copper alloy seedlayer by electroplating.
 14. The method of claim 13, wherein aluminum ispresent in the copper alloy seed layer in a concentration between about0.01 weight percent and about 5 weight percent.
 15. A structure,comprising: a substrate having a dielectric layer formed thereon, thedielectric layer having an aperture formed therein; a barrier layerformed over the dielectric layer; and a copper alloy seed layer formedover the barrier layer, the copper alloy seed layer comprising analloying material selected from the group of aluminum, magnesium, andcombinations thereof, the alloying material being present in the copperalloy seed layer in a concentration between about 0.01 weight percentand about 10 weight percent.
 16. The structure of claim 15, wherein thealloying material is present in the copper alloy seed layer in aconcentration between about 0.01 weight percent and about 5 weightpercent.
 17. The method of claim 15, wherein the barrier layer comprisesa material selected from the group consisting of tantalum nitride,tantalum, titanium, titanium nitride, tungsten, tungsten nitride, otherrefractory metals, other refractory metal nitrides, and combinationsthereof.
 18. The structure of claim 15, further comprising a bulk copperlayer formed over the copper alloy seed layer.
 19. A structure,comprising: a substrate having a dielectric layer formed thereon, thedielectric layer having an aperture formed therein; a barrier layercomprising tantalum nitride formed over the dielectric layer; a copperalloy seed layer formed over the barrier layer, the copper alloy seedlayer comprising aluminum present in the copper alloy seed layer in aconcentration between about 0.01 weight percent and about 10 weightpercent; and a bulk copper layer formed over the copper alloy seedlayer.
 20. The structure of claim 19, wherein aluminum is present in thecopper alloy seed layer in a concentration between about 0.01 weightpercent and about 5 weight percent.